1. Field of the Invention
The present invention relates to an inkjet printer.
2. Description of the Related Art
Conventionally, an inkjet printer for large format printing that includes a plurality of recording heads arrayed in a direction perpendicular to a scanning direction of a head unit is known. The inkjet printer having such a structure performs printing on a large area of a recording medium within a short time. Japanese Laid-Open Patent Publication No. 2013-67031 discloses an inkjet recording device including a plurality of head units arrayed in the scanning direction. The plurality of head units each include a plurality of recording heads arrayed in a feeding direction perpendicular to the scanning direction.
Some recording mediums such as cloth, paper and the like are not white. In the case where process color ink is directly injected onto such a non-white recording medium, the real color of the ink may not be provided. According to a technique for dealing with this situation, a recording head injecting white ink is added to the printer described in Japanese Laid-Open Patent Publication No. 2013-67031. With this technique, first, a white ink layer is formed on the recording medium. After the white ink layer is formed on the recording medium, an image layer of process color ink is formed on the white ink layer. In this manner, a color close to the real color of the ink can be printed even on a recording medium that is not white.
Usually, the above-described technique provides a sufficiently high level of image quality even on a recording medium that is not white. However, a still higher level of image quality may be desired for some uses of the printed item. In the field of, for example, outdoor advertisements or the like, there is a need for an image giving a strong impression of having depth or massiveness in order to attract more attention. However, often times, the conventional printing method does not fulfill such a need. A reason for this is that the image layer is thin and thus the influence of special color ink forming the underlying color layer is not completely eliminated. For example, in the case where the special color ink is white ink, the image appears whitish and thus lacks massiveness. In order to deal with such a situation, the present inventors conceived of a method of printing an underlying color layer with a portion of an image being mixed in the underlying color layer. More specifically, according to this method, a portion of ink dots of process color ink used to form the image is extracted by use of a mask and printed concurrently with the underlying color layer, and then the image is printed as being piled up on the underlying color layer. The present inventors have discovered that the above-described method can provide printing with more massiveness than by conventional piled-up printing.
However, a printed item provided by the above-described method may involve the following problem. The image printed as being mixed in the underlying color layer (hereinafter, such an image will be referred to as an “underlying image”) is formed of a portion of the ink dots of the process color ink. Therefore, as seen on an ink dot-by-ink dot basis, the printed item includes points to which the ink has been injected and points to which the ink has not been injected. For this reason, an extraction pattern including the points to which the ink has been injected and the points to which the ink has not been injected may be visually recognized as a graphical pattern. The graphical pattern appears because a portion of the ink dots is extracted and the remaining portion of the ink dots is not extracted. Even after the image to form an upper layer (hereinafter, such an image will be referred to as a “subject image”) is printed as being piled up on the underlying image, the graphical pattern may still appear.